Mr McAteer said he was due to meet with Mr Pfahl shortly after he arrived home from the cruise to attend a football game back in London.

"He was incredibly ambitious, a mentor to so many people who loved his family. He had his own band. He was incredibly charismatic who inspired everyone around him.

"I have huge respect for JP, (he) always had incredible ideas and I loved hanging out with him. I am truly shocked and saddened.

"The world has lost a brilliant, innovative and caring family man who was an inspiration to everyone around him."

Mr Pfahl moved to London in 2005 to pursue his career in finance. In an interview with UK website Australian Times, the businessman said his first investment was "into a three-month mentoring program with a multi-millionaire property investor".

In the 2015 interview, Mr Pfahl spoke of his Australian wife, and while he loves to visit Sydney, "London is home".

The man allegedly plunged into the water in the early hours of Wednesday when the Royal Caribbean's Symphony of the Seas ship was en route to Saint Thomas.

The Symphony of the Seas. Picture: Royal Caribbean

Another friend, Karen Gould, said Mr Pfahl - who was nicknamed JP - was a " mentor", a "great rock star" and "loved life".

"I am devastated by the news," Ms Gould, who was also on holiday when she found out about Mr Pfahl's passing, told news.com.au.

"He was a loyal friend who believed in me when I had lost faith in myself. I went on to become his friend and worked for him.

"He was a great entrepreneur who inspired many other young entrepreneurs with his inspiration and motivation. He was a loving father and husband and he did live life like a rock star. He was known as JP the legend."

Friends said he was often nicknamed JP the rock star Source:Facebook

The US Coast Guard said it wouldn't investigate the incident as the ship was registered to the Bahamas, the man was not a US citizen and the death happened in international waters, the Miami Herald reported.

The ship was on a seven-day cruise through the eastern Caribbean and was due to return to Miami, Florida on Saturday. The man's body will remain on the ship until it returns to Miami.

Last year, 23 people went overboard on cruise ships and only four bodies were found, according to the Herald.

Mr Pfahl, a former student of Sydney’s Knox Grammar School and the University of Sydney, founded the company Rockstar Group.